Drilling instrument in particular for drilling dental root canals

ABSTRACT

The invention concerns a drilling instrument ( 10 ), in particular for drilling dental root canals comprising a base ( 11 ) and a guide section ( 13 ) as well as a polygonal cutting section ( 12 ). Said cutting section includes several helical cutting edges ( 17 ) defining an envelope ( 15 ). The flutes ( 14 ), which are the surfaces linking in the cutting edges, are cut out such that part of them define clearance zones ( 16   a ) alternately arranged between the drilling zones ( 16   b ). In the central part of a clearance zone ( 16   a ), the cutting edges ( 17 ) are all arranged recessed inside the envelope ( 15 ), in the central part of the drilling zone ( 16   b ), said cutting edges are all arranged on the envelope, and in a zone intermediate between a clearance zone ( 16   a ) and an adjacent drilling zone ( 16   b ), at least one cutting edge is on the envelope and at least one cutting edge is recesses inside the envelope.

This application is a National Stage Application of PCT/CH02/00098 whichclaims priority from FR 01/02452 filed Feb. 20, 2001.

FIELD OF THE INVENTION

The present invention concerns a drilling instrument, in particular fordrilling dental canals in the framework of dental root treatment, thisinstrument including a base, a cutting section and a guiding section,the cutting section being defined by an envelope cylindrical or conicalin shape, this cutting section being provided with clearance zones,placed so that they are set back relative to the envelope, alternatingwith drilling zones placed on the envelope.

BACKGROUND OF THE INVENTION

Currently, most of the dental canal drilling instruments have a cuttingpart called a cutting section with a conical envelope and including oneor more cutting edges wound up into a helix along this cutting part.

This helical shape is indispensable for removal of debris from teetharound the outside of the root. During use, the conical part may undergoa coating phenomenon when the instrument is introduced into the rootcanal and when it is carried along in rotation. It may happen that itbecomes bound in the root canal. For this reason, it is recommended touse such an instrument only with manual axial movement possibly with aslight movement in rotation alternating in one direction and in thereverse direction. Otherwise, the instrument may be blocked in the toothand break. Breaking the instrument may cause serious consequences giventhat a dental canal is narrow and that access to it is difficult.

There are certain instruments for which the tendency towards binding hasbeen partially eliminated. In particular, this has been obtained bygreatly blunting the cutting angles. This type of instrument may be usedwith a rotating drive motor turning at low speed so as not to deform thenatural path of the canal while enlarging it.

The fact that the cutting edges may be blunted presents a drawback forseveral reasons. On the one hand, the cutting work necessary to enlargethe dental canal is carried out with difficulty. On the other hand, thefriction between the blunted edges and the walls of the canal causessignificant working torque, which may also cause the instrument tobreak. In order to avoid this risk, it is necessary to use a whole rangeof instruments with different conicities, those having the greatestconicity being used first. In this case, the coating effect iseliminated and the restraints due to friction caused on the instrumentremain less than the breaking limit. However, the work is only appliedto a delimited part of the dental canal.

With most of the known motorized drive instruments the gain in timerelative to the manual method is not certain and the risks of breakingremain high.

Various instruments of this type have been the object of patents. TheU.S. Pat. No. 6,074,209 precisely describes one of these instruments inwhich the edges are rounded. It includes zones with narrow cross sectionwhich alternate with zones of larger cross section. The zones of narrowcross section are obtained by grinding the part in predetermined placesof a blank in which the section is initially constant if the instrumentis cylindrical, or regularly decreasing if the instrument is generallyconical in shape which causes passages between the zones with narrowcross section and zones with larger cross section to sharp transverseedges which risk catching on the walls of the canal and blocking theinstrument.

The international application published as WO 00/59399 describes aninstrument of this type made by twisting an elongated piece with ageneral conical shape and in which the cross section is rhomboidal inshape. It is also the case with the instrument described in U.S. Pat.No. 4,260,379. The rhombus has a large diagonal and a small diagonal,the instrument is made twisting a piece in which the section is arhomboid and includes alternating zones of reduced cross section andlarger cross section corresponding respectively to the small and largediagonal of the rhombus. The zones with different section are not movedalong the instrument but they are angularly moved by 90 degrees. It isnoted that this geometry does not allow avoidance of the bindingphenomenon of the instrument and that certain restraints exerted on thisinstrument could cause its breaking.

SUMMARY OF THE INVENTION

The present invention proposes to improve the drawbacks of the drillinginstruments of prior art by offering an instrument in which the risk ofbinding is eliminated while maintaining a relatively low torque, thusavoiding premature fatigue.

These goals are reached by an instrument as defined in the preamble andcharacterized in that the cutting section is polygonal in cross sectionand includes sharp edges, in that in the central part of a clearancezone said edges are all placed so as to be set back within saidenvelope, in that in the central part of a drilling zone, these edgesare all placed on said envelope and in which, in an intermediate zonebetween a clearance zone and an adjacent drilling zone, at least oneedge is on the envelope and at least one edge is set back within theenvelope.

According to a preferred embodiment, the axis of the cutting section ismoved forward relative to the axis of said envelope. This axis of thecutting section is helicoidal and is wound up into a helix around therectilinear axis of the envelope, in order to make the removal zonesdeeper and more effective.

Particularly advantageously, an intermediate zone located between thecentral part of a clearance zone and the central part of an adjacentdrilling zone is divided into n segments where n corresponds to thenumber of edges of the cutting section, and along each of these segmentsthe number of edges placed on the envelope is increased by a unit in thedirection going from a clearance zone towards the adjacent drillingzone.

In the specific case where said cutting section has a triangular crosssection, an intermediate zone located between the central part of aclearance zone and the central part of an adjacent drilling zone ispreferably divided into three segments, and along each of these segmentsthe number of edges placed on the envelope goes successively from zeroto one, then to two and finally three in the direction going from aclearance zone towards the adjacent drilling zone.

According to a particularly advantageous embodiment, at least one flute,which is the surface delimited by two edges of the cutting section, isovertrimmed relative to the others so as to form said clearance zones.

In the case where the cutting section includes four cutting edges, theseedges define four flutes which are placed at approximately right angles.

Preferentially, said instrument is used in the odontology field and thedimension of the clearance zone are 0.1 mm less than that of thedrilling zone.

When the cross section of the cutting section is triangular, its shapeis preferentially that of an equilateral triangle.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be better understood inreference to the following description of different embodiments of theinvention and to the attached drawings in which:

FIG. 1 is a view of the entire instrument according to the presentinvention;

FIG. 2 is an enlarged view of a central part of the instrument of FIG. 1and corresponding to the cutting section;

FIGS. 3A and 3D are cutaway views along lines A—A and B—B of FIG. 2,respectively, illustrating the variation in the contour of the cuttingsection, FIGS. 3B and 3C being views intermediate between these twopositions;

FIG. 4 is a cutaway view illustrating a specific embodiment of thecutting section, and

FIG. 5 represents another shape for production of the instrumentaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In reference to the figures, the drilling instrument 10 according to thepresent invention includes a base 11, a cutting section 12 and a guidingsection 13. Base 11 is conventional and may have a cylindrical orconical shape, with a circular or polygonal cross section, especially asquare or triangular one. The guiding section 13 is also formedconventionally and is ended by a rounded point allowing easyintroduction into the drilling to be treated [sic] and in particularinto a dental canal. In the example illustrated by FIG. 1, the guidingsection 13 presents a certain conicity that allows the operator toeasily follow the natural tracing of the canal with a view to enlargingit by means of the cutting section 12.

The cutting section 12 has a new shape relative to the cutting sectionsof existing instruments. In the illustrated examples, it is polygonal insection and includes sharp edges. More specifically, in the exampleillustrated by FIGS. 1 to 4, it includes a triangular cross sectionforming sharp edges 17 a, 17 b and 17 c, defining three flutes 14helicoidal in shape which are placed within an approximately truncatedenvelope 15 , a flute being the surface bounded by two edges of thecutting section 12. This cutting section 12 includes clearance zones 16a placed so that it is set back relative to the envelope 15 and whichalternate with the drilling zones 16 b placed on the envelope 15 , thedimension of the clearance zone 16 a being 0.1 mm less than that of thedrilling zone 16 b.

As shown in FIG. 3A, which is a cutaway view in the central part of thedrilling zone, the edges 17 a, 17 b and 17 c are all placed on saidenvelope 15 and, as shown in FIG. 3D, which is a cutaway view in thecentral part of a clearance zone, these edges are all placed so thatthey are set back within said envelope 15. FIGS. 3B and 3C show that inan intermediate zone between the clearance zone and an adjacent drillingzone, at least one edge 17 b and/or 17 c is on the envelope and at leastone edge 17 a and/or 17 b is set back within the envelope 15.

Since the cross section of the cutting section 12 has a polygonal shape,the number of its edges being n, and considering that an intermediatezone located between the central part of a clearance zone 16 a and thecentral zone of an adjacent drilling zone 16 b is divided into nsegments, when one moves along each of these segments, the number ofedges placed on the envelope 15 is increased by a unit in the directiongoing from a clearance zone towards the adjacent drilling zone. In thisway, the passage of the edges from their position on the envelope 15towards a position that is set back relative to this envelope is carriedout continuously and uniformly.

When said cutting section 12 has a triangular cross section, anintermediate zone located between the central part of a clearance zone16 a and the central part of an adjacent drilling zone 16 b is dividedinto three segments and along each of these segments, the number ofedges placed on the envelope goes successively from zero to one, then totwo and finally to three in the direction going from a clearance zone 16a towards an adjacent drilling zone 16 b.

To create this geometry by means of grinding equipment, at least oneflute 14 is overtrimmed locally compared with others so as to form saidclearance zones 16 a. At least one part of one of the flutes is trimmedso that it is not tangential to the envelope.

A variant illustrated by FIG. 4 makes it possible to again increase theeffectiveness of the clearance zones. According to this embodiment, theaxis 20 of envelope 15 is moved a distance e from axis 21 of the cuttingsection 12. Axis 20 of the envelope is rectilinear and axis 21 of thecutting section is helicoidal and is wound up into a helix around axis20. The embodiment makes it possible to deepen the clearance zones andto make them more effective for carrying material during treatment.

In the example illustrated by FIG. 5, the cutting section 12 isrectangular in cross section and therefore includes four sharp edges 16which define four flutes 19 placed approximately at right angles. Inthis embodiment, two opposing flutes may be overtrimmed.

These embodiments present numerous advantages relative to similarinstruments of the prior art. On the one hand, the instrument is easy tomachine since the existence of a clearance zone spaced between theenvelope and one or more flutes practically does not modify theproduction procedure which is based on the relative displacement of theabrasive wheels and the blank of the instrument in an automatic andprogrammed way.

In addition, they absolutely avoid any risk of binding of theinstrument. Thus, it is possible and even desirable to keep a sharpcutting edge. This makes excellent machining of the material possiblewhile avoiding heating of the instrument and while maintaining arelatively low torque. The lifetime of the instrument is thus found tobe increased and the risk of breakage is greatly decreased.

The decrease of the torque also makes it possible to use a relativelyflexible instrument which ensures it good guiding into a curved dentalcanal.

As the risk of binding is zero, it is not necessary to use a large rangeof instruments with different conicities which decreases the cost of thematerial necessary for the treatment on the one hand, and the length oftreatment on the other.

INDUSTRIAL APPLICATION POSSIBILITIES

The present invention has been described essentially in an applicationin odontology, with a drill essentially conical or cylindrical in shape.Other shapes of drills could also be used. In particular, it is possibleto apply the invention to drills of known types with the names “Gate,”“Peeso” or cylindrical drills, as well as for known cutters for pins,with an overtrimmed shaft or “fissure.”

The helical pitch of the flutes, their number and the dimension of theclearance zones are not limited and it is possible to modify themwithout leaving the scope of the present invention.

It is also possible to use the instrument that is the object of theinvention in fields other than odontology, especially in surgery and inparticular in orthopedics, as well as in fields such as mechanics forworking metals or synthetic materials, carpentry or working with woodand similar materials. This especially makes it possible to make drillsfor manual use in which there is no risk of binding.

What is claimed is:
 1. Endodontic instrument comprising: a base (11), acutting section (12) and a guiding section (13), the cutting sectionbeing defined by an envelope (15) of cylindrical or conical shape, thiscutting section being provided with clearance zones (16 a), located sothat said clearance zones are set back relative to the envelope (15),alternating with drilling zones (16 b) placed on said envelope, thecutting section (12) is a polygonal in cross section and includes sharpedges, and in a central part of a clearance zone (16 a) said edges areall placed so that said edges are set back from the envelope (15),wherein the central part of a drilling zone (16 b), said edges are allplaced on said envelope and in a zone intermediate between a clearancezone (16 a) and an adjacent drilling zone (16 b), at least one edge ison the envelope and at least on edge is set back from the envelope. 2.Endodontic instrument according to claim 1, wherein an axis (21) of thecutting section (12) is moved relative to an axis (20) of said envelope(15).
 3. Endodontic instrument according to claim 2, wherein the axis(21) of the cutting section (12) is helicoidal and turns around therectilinear axis (20) of the envelope (15).
 4. Endodontic instrumentaccording to claim 1, wherein an intermediate zone located between thecentral part of a clearance zone (16 a) and the central part of anadjacent drilling zone (16 b) is divided into n segments where ncorresponds to the number of edges of the cutting section (12), and inthat along each of said segments the number of edges placed on theenvelope (15) is increased by a unit in the direction going from aclearance zone (16 a) towards the adjacent drilling zone (16 b). 5.Endodontic instrument according to claim 4, in which said cuttingsection (12) has a triangular cross section, wherein an intermediatezone located between the central part of a clearance zone (16 a) and thecentral part of an adjacent drilling zone (16 b), is divided into threesegments and in that along each of these segments, the number of edgesplaced on the envelope goes successively from zero to one, then to twoand finally to three in the direction going from a clearance zone (16 a)toward the adjacent drilling zone (16 b).
 6. Endodontic instrumentaccording to claim 5, wherein at least one flute (14), which is thesurface bounded by two edges of the cutting section (12), is overtrimmedrelative to the others so as to form said clearance zones (16 a). 7.Endodontic instrument according to claim 1, wherein the cutting section(12) includes four cutting edges (18), which define four flutes (17)placed approximately at right angles.
 8. Endodontic instrument accordingto claim 1, used in the field of odontology, wherein a dimension of theclearance zone (16 a) is 0.1 mm less than that of the drilling zone (16b).
 9. Endodontic instrument according to claim 1, wherein the cuttingsection (12) has a cross section with the shape of an equilateraltriangle.
 10. Endodontic instrument according to claim 1, wherein thecutting section (12) has a cross section that is approximately square inshape.